Spinopelvic Imbalance Is Associated With Increased Sway in the Center of Gravity: Validation of the “Cone of Economy” Concept in Healthy Subjects

STUDY DESIGN: Cross-sectional study. OBJECTIVES: To investigate the effects of pelvic compensation on standing balance in healthy volunteers. METHODS: The 180 healthy volunteers were recruited at a basic health checkup. The inclusion criteria were: 1) age ≥ 65 years, 2) underwent a whole spine radiograph and stabilometry, 3) well-balanced standing posture with a sagittal vertical axis <50 mm, and 4) a visual analog scale of lower back pain of <20 mm. Based on the pelvic incidence (PI) and lumbar lordosis (LL) mismatch, subjects were divided into harmonious (PI–LL ≤ 10°) or unharmonious (PI–LL > 10°) groups. RESULTS: Participants in the unharmonious group were significantly older compared with the harmonious group (70.2 ± 4.4 vs. 72.0 ± 4.6 years, P < .01). The PI minus LL values were −2.2° ± 7.5° and 16.6° ± 7.0° in the harmonious and unharmonious groups, respectively (P < .001). Anteroposterior LNG/TIME (average center of pressure sway speed) was significantly greater in the unharmonious group with both open and closed eyes (1.04 ± 0.38 cm/s vs. 1.25 ± 0.47 cm/s, P < .001 and 1.22 ± 0.54 cm/s vs. 1.58 ± 0.77 cm/s, P < .001, respectively). Lateral LNG/TIME was significantly greater in the unharmonious group only with closed eyes (1.24 ± 0.54 cm/s vs. 1.47 ± 0.79 cm/s, P = .03). CONCLUSIONS: Healthy elderly subjects with poor spinopelvic harmony had relatively unstable standing balance. The “cone of economy” was demonstrated, showing that unharmonious spinopelvic balance had a non-economic effect on standing.